Reports have been made on widely acceptable processes for preparing 3-halogenated cephem derivatives represented by the formula (2). These processes include a process which uses a compound of the formula (3), i.e., 3-hydroxycephem compound and involves the conversion of hydroxyl group to trifluoromesyloxy group first and the subsequent reaction with a lithium halide J. Org. Chem., 54, 4962(1989)!, and a process wherein a reactive chlorine or bromine compound (such as phosphorus trichloride, phosphorus oxychloride or thionyl bromide) is reacted with a 3-hydroxycephem compound in dimethylformamide (JP-A-116095/1974). ##STR3## wherein R.sup.1, R.sup.2 and R.sup.3 are as defined below.
These processes requires the use of the 3-hydroxycephem compound as the starting material which compound itself is difficult to prepare, so that the process is in no way industrially feasible.
Further, a process is known wherein an allenyl .beta.-lactam compound of the formula (1) is reacted with a halogen salt of alkali metal or alkaline earth metal to cyclize the allenyl .beta.-lactam compound to obtain the 3-halogenated cephem compound (JP-A-282387/1992). This process is advantageous in employing the starting material, allenyl .beta.-lactam compound, which is easily available, but inevitably forms 3-sulfonylcephem as a by-product due to the recombination of sulfinate ion which is released on ring closure, consequently giving the desired 3-halogenated cephem derivative in a yield of as low as up to 70% .
An object of the present invention is to provide a process for preparing the desired 3-halogenated cephem derivative in a high yield with a high purity by a safe and simplified procedure without using a starting material which is difficult to prepare.